Ceramic electron tube



Sept. 27, 1955 5 SORG ET AL 2,719,185 CERAMIC ELECTRON TUBE Filed Jan.23, 1951 2 Sheets-Sheet l WWW mmm

I N V EN TORS Ham/a E. Sorg By Huber? /7'. faves Donald E Dr/es rvman nME ATTORNEY Sept. 27, E SORG ET AL CERAMIC ELECTRON TUBE 2 Sheets-Sheet2 Filed Jan. 23, 1951 5 R m W a m E M United States Patent CERAMICELECTRON TUBE Harold E. Sorg, Redwood City, Hubert H. Eaves, Palo Alto,and Donald F. Drieschman, Los Altos, Calif., assignors toEitel-McCullough, Inc., San Bruno, Calif., a corporation of CaliforniaApplication January 23, 1951, Serial No. 207,302

Claims. (Cl. 174-5053) Our invention relates to electron tubes and moreparticularly to tubes having ceramic envelopes such as disclosed in ourcopending United States Letters Patent 2,647,218 granted July 28, 1953.

It is among the objects of our invention to provide further improvementsin a tube wherein the envelope comprises ceramic sections metallicallybonded together and in which the metallic bonds serve as lead inconductors for the electrodes.

Another object is to provide such a tube having its envelope built up ofvertically disposed coaxial ceramic sections, the sections beingpreferably interfitted at the joints for alignment.

Another object is to provide a tube of the character described whereinthe electrode terminals comprise metalized areas on the outer surfacesof the ceramic sections, and in which the sections have differentexternal diameters to provide offset coaxial terminals.

A further object is to provide a tube structure having improvedelectrical, thermal and mechanical properties, and which is particularlywell adapted for economical manufacture.

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be set forth in the followingdescription of our invention. It is to be understood that we do notlimit ourselves to this disclosure of species of our invention, as wemay adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

Figure 1 is a side elevational view of a tube embodying the improvementsof our invention; and

Figure 2 is a vertical sectional view of the same.

Figure 3 is a fragmentary view showing a modified terminal construction.

In terms of broad inclusion our improved electron tube comprises anenvelope made up of ceramic sections metallically bonded together at thejoints, the external terminal being preferably formed by metalized areason the ceramic sections and connected to the internal electrodes throughthe metallic bonds. velope sections are preferably coaxial andvertically disposed, the outer cylindrical surfaces of the sectionsbeing of different diameters decreasing in size toward the lower end ofthe envelope to provide offset coaxial terminals for the electrodes. Inour preferred construction the envelope sections are interfitted at thejoints, as by recessed edges, to facilitate alignment during assembly.The tube structure embodying our invention is particularly well adaptedfor tubes having a number of electrodes, such as triodes or tetrodes,and especially to such tubes having planar type electrodes.

In greater detail and referring to Figures 1 and 2 of the drawings, weshow a planar electrode tetrode for purposes of illustration. Theimproved tube comprises an evacuated envelope made up of verticallydisposed coaxial sections of ceramic, namely, an upper ring-shapedsection 2, a lower stem section 3, and three cylindrical The ceramicenside wall sections 4, 6 and 7 interposed between the end sections. Theenvelope is thus built up of a series of vertically stacked ceramicsections, which sections are coaxial about the central axis of the tube.The envelope sections have outer cylindrical surfaces of differentdiameters decreasing in size toward the lower end of the envelope forthe purpose of providing offset coaxial terminals as hereinafterdescribed.

In order to facilitate assembly, the ceramic envelope sections arepreferably interfitted at the joints for selfalignment of the parts whenthe sections are stacked together. to provide annular seats forreceiving adjacent sections, as seen in Figure 2. The several sectionsare thus seated one against the other, which serves to align the partscoaxially and vertically.

The ceramic envelope sections in our tube are metallically bondedtogether at the joints to form vacuumtight seals; the stem and wallsections 3 and 7 being united by a metallic bond 8, the wall sections 7'and 6 being united by a metallic bond 9, the wall sections 6 and 4 beingunited by a metallic bond 11, and the wall and upper sections 4 and 2being likewise united by a metallic bond 12. These metallic bondinglayers extend along the abutting surfaces between the parts from theinside to the outside of the envelope and also function as lead-inconductors for the electrodes as hereinafter described in greaterdetail.

The ceramic used in making up the envelope may be of any suitableceramic-like material, such as the alumina or zircon type ceramic bodiescommercially available. We prefer the alumina or zircon type bodiesbecause their mechanical strength, thermal resistance and electricalinsulating properties are favorable, although other type ceramics arealso satisfactory.

Metallic bonds 8, 9, 11 and 12 forming the vacuumtight seals may be madein several ways, utilizing known metallizing and brazing techniques. Forexample, the opposed surfaces of the ceramic pieces may be coated withfinely divided molybdenum powder, or a mixture of molybdenum and ironpowders or the like, and then fired in hydrogen to a temperature ofabout 1500 C. to sinter the metal powder to the ceramic surface. Thisproduces a thin metallic layer firmly bonded to the ceramic. Suchmetalized surfaces may then be brazed or soldered together with silversolder or brazing alloys such as silver-copper, gold-copper or the like.The brazes are readily made by fitting the metalized ceramic piecestogether with rings of wire solder adjacent the joints, and thenelevating the temperature of the whole up to the melting point of thesolder in a suitable furnace. Another metalizing technique is to painttitanium or zir conium hydride powders on the surfaces of the ceramicparts and fire in vacuum to about 1200 C.-, after which the metalizedsurfaces may be brazed together with silver solder or the like. Weprefer the molybdenum sintering process because it does not require avacuum furnace for the firing operation.

In the tube illustrated having an indirectly heated cathode the lattercomprises a cup-shaped cathode sleeve 13 such as nickel enclosing asuitable heater 14, the end of the cathode sleeve being coated with anelectron emissive material such as the conventional bariumstrontiumoxides. In our preferred construction the cathode is supported by theceramic stern section 3 which projects into the envelope for thatpurpose, the cathode sleeve being fitted on the reduced inner end of thestem. A convenient heater structure comprises a flat helix of wireembedded in a suitable insulating material carried by a cup-shaped liner17 pressed into the cathode sleeve, one end of the heater wire beingconnected to This is accomplished by recessing the sections 3 thecathode sleeve and the other end brought out by a lead 13 through a holein the stem and connected to a cup-shaped metal terminal 19 brazed to areduced end of the ceramic stem section.

As hereinbefore mentioned, the metallic bonds between the ceramicsections are utilized as lead-in conductors to the electrodes. In thecase of the cathode the bond 8 serves as the lead-in conductor. Anotherfeature in our construction is that the external terminals on theenvelope as well as the internal connections to the electrodes arepreferably formed by metalized areas on the ceramic sections. Thus, whenthe ceramic stem 3 is treated, as by molybdenum sintering, to metalizethe region adjacent the joint, it is also preferably metalized oversubstantially its entire length so as to simultaneously provide theexternal cathode terminal 21 and the internal connection 22, the cathodesleeve 13 being connected or brazed directly to the metalized area 22.

Control grid 23 of the tetrode illustrated lies transversely across theenvelope above the cathode and comprises parallel grid wires fastened toa metal ring 24. The control grid is supported by side Wall section 7 ofthe envelope, section 7 projecting internally to provide a flat ledgefor that purpose. Metallic bond 9 serves as the lead-in conductor forthe control grid and the external terminal 26 as well as the internalconnection 27 are formed by metalized areas on the ceramic section 7.Thus, when section 7 is treated to metalize the region adjacent thejoint, the metalized areas are preferably extended to provide anexternal band on the outer cylindrical surface for the grid terminal 26and an internal band on the inner flat ledge for the grid connection 27,the grid ring 24 being connected or brazed directly to the metalizedarea 27.

Screen grid 28 also lies transversely across the envelope and comprisesparallel Wires fastened to a metal ring 29, the screen grid beingsupported by side wall section 6 which has an inwardly projecting ledgefor that purpose. Metallic bond 11 serves as the lead-in conductor forthe screen grid, and the external terminal 31 as well as the internalconnection 32 are formed by metalized areas on the ceramic section 6.Thus, when section 6 is treated to metalize the region adjacent thejoint the metalized areas are preferably extended to provide an externalband on the outer cylindrical surface for the screen grid terminal 31and an internal band on the inner flat ledge for the screen gridconnection 32, the grid ring 29 being connected or brazed directly tothe metalized area 32.

The metal anode 33, say of copper, preferably projects into the envelopethrough the upper ring-shaped section 2 and is supported on the latterby a metal sealing flange 34. Exhaust tubulation 36 is preferablymounted on the anode and outwardly projecting portion 37 of the anodepreferably carries a suitable cooler 38. Metallic bond 12 serves as thelead-in conductor for the anode and the external terminal 39 as well asthe internal connection 41 are formed by metalized areas on the ceramicsection 2. Thus, when section 2 is treated to metalize the regionadjacent the joint, the metalized areas are preferably extended toprovide an external band on the outer cylindrical surface for the anodeterminal 39 and an internal band on the inner surface for the anodeconnection 41, the anode sealing flange 34 being brazed directly to themetalized area 41.

The brazes at the joints and metalized areas for the terminals are shownas having appreciable thickness for convenience of illustration.Actually these are quite thin metallic layers, say of the order of0.002" to 0.005" thickness, and appear as films or metal skins on thesurfaces of the ceramic. If desired, silver, copper or the like may beflowed or electroplated over the sintered areas to further improve theelectrical conductivity of such areas. Copper plating on the sinteredareas, for example, makes excellent terminal surfaces and is ideal forbrazing the surfaces together at the joints either with or without theuse of additive brazing material.

Since the several electrode terminals 39, 31, 26 and 21 are on the outercylindrical surfaces of the ceramic sections, which surfaces are ofdiflerent diameters decreasing in size toward the lower end of theenvelope, it will be seen that our structure provides offset coaxialterminals on the tube. As clearly shown in Figures 1 and 2, the anodeterminal 39 is on a surface of larger diameter than that of the cathodeterminal 21, and screen and control grid terminals 31 and 26 are onsurfaces of intermediate diameter. Such terminal arrangement isparticularly well suited for coaxial type cavity circuits used in highfrequency work.

Our improved tube construction eliminates the metal pieces which usuallyhave to be interposed in a tube envelope, and provides a substantiallyall-ceramic envelope. The tube is extremely strong mechanically and hasexcellent thermal resistance properties for high temperature operation.Another important feature is that excellent paths for radio-frequencycurrent are provided for circuit connections to the electrodes, whichpaths are short, direct and of low loss. These advantages together withthe coaxial terminal arrangement all contribute to make the tube ideallysuited for operation at the ultra-high frequencies. Still anotherimportant advantage of our tube is that it is easy to assemble and iswell adapted for economical high speed production. The interengagingfeature at the joints of the ceramic sections, so that the envelope canbe accurately assembled by simply stacking the sections together,contributes to the ease of tube fabrication. In our tube the metalizedenvelope sections are stacked together with rings of suitable brazingmaterial adjacent the joints and the entire assembly placed in a furnacefor brazing in one opera tion.

Mounting of the electrodes directly on the ceramic sections eliminatesinternal hardware and still further improves the tube for operation atthe higher frequencies.

Furthermore, and this is important, the ceramic envelope sections may beaccurately sized, even by finish grinding if desired, to precisely andaccurately establish the spacings between the electrodes, such as thecathodeto-grid, grid-to-grid and grid-to-anode spacings. With precisionmade envelope sections, which is possible in our construction, and withthe interengaging feature at the joints which self-aligns the sectionsboth concentrically and longitudinally, it will be seen that thespacings between the electrodes are under precise control duringassembly of the tube. All of this is achieved without requiring specialjigs or skilled operators. Another advantage, since the envelopesections are made of the same kind of material having the samecoefficient of expansion, is that mechanical stresses between the partsduring temperature fluctuations are minimized. Thus, envelope cracks,seal failures and other undesired effects are avoided which frequentlyoccur in conventional tubes where different kinds of materials are usedin envelope constructions.

Figure 3 is a fragmentary view of the stem section showing a modifiedterminal arrangement in which a metal sleeve 42 is brazed to theexternal metalized area of the stem to provide the cathode terminal,which sleeve is thus connected to the electrode via the braze 8 aspreviously described. Similar sleeves may likewise be provided on theother sections for the grid and anode terminals. Such sleeved terminalconstruction is desirable in some cases Where a heavier terminalstructure is desired although the metalized terminal surface firstdescribed is simpler and adequate in most instances.

While we have illustrated our improvements in connection with a tetrodehaving planar electrodes, it is understood that the structure is wellsuited for tubes having other internal electrode assemblies such astriodes or pentodes, or tubes having cylindrical instead of planarelectrodes. Likewise, our improvements may be incorporated in tubeshaving radiation cooled internal anodes as well as tubes havingexternally cooled anodes, as will be readily appreciated.

We claim:

1. An electron tube having an envelope comprising a series of verticallystacked coaxial sections of ceramic fitted together at joints betweenthe sections, said sections having abutted portions at the joints toestablish vertical alignment of the stacked sections, metallic bondsuniting the ceramic sections at the joints, said sections having outercylindrical surfaces of different diameters decreasing in size toward anend of the envelope, metalized areas on said cylindrical surfacesproviding exposed offset c0- axial terminals, and electrodes in theenvelope connected to the terminals through said metallic bonds.

2. An electron tube having an envelope comprising a series of verticallystacked coaxial sections of ceramic fitted together at joints betweenthe sections, said sections having telescoping portions at the jointsestablishing coaxial alignment of the stacked sections, metallic bondsuniting the ceramic sections at the joints, said sections having outercylindrical surfaces of different diameters decreasing in size toward anend of the envelope, metalized areas on said cylindrical surfacesproviding exposed offset coaxial terminals, and electrodes in theenvelope connected to the terminals through said metallic bonds.

3. An electron tube having an envelope comprising a series of verticallystacked coaxial sections of ceramic fitted together at joints betweenthe sections, said sections having partially abutting and partiallytelescoping portions at the joints establishing both vertical andcoaxial alignment of the stacked sections, metallic bonds uniting theceramic sections at the joints, said sections having outer cylindricalsurfaces of different diameters decreasing in size toward an end of theenvelope, metalized areas on said cylindrical surfaces providing exposedoffset coaxial terminals, and electrodes in the envelope connected tothe terminal through said metallic bonds.

4. An electron tube having an envelope comprising a series of verticallystacked coaxial sections of ceramic fitted together at joints betweenthe sections, metallic bonds uniting the ceramic sections at the joints,metalized areas on outer cylindrical surfaces of the ceramic sectionsproviding terminals, and electrodes in the envelope connected to theterminals through said metallic bonds, said electrodes having activesurfaces disposed in spaced horizontal planes and each electrode beingsupported by a different ceramic section of the envelope, said sectionshaving abutting portions along horizontal planes at the joints toestablish vertical alignment of the stacked sections and to fix thespacing between the electrodes.

5. An electron tube having an envelope comprising a series of verticallystacked coaxial sections of ceramic fitted together at joints betweenthe sections, metallic bonds uniting the ceramic sections at the joints,metalized areas on outer cylindrical surfaces of the ceramic sectionsproviding terminals, and electrodes in the envelope connected to theterminals through said metallic bonds, said electrodes having activesurfaces disposed in spaced horizontal planes and each electrode beingsupported by a different ceramic section of the envelope, the envelopesections having inwardly projecting portions providing flat supportingledges for the electrodes, said sections having abutting portions alonghorizontal planes at the joints to establish vertical alignment of thestacked sections and to fix the spacing between the electrodes.

References Cited in the file of this patent UNITED STATES PATENTS2,035,015 Schirmer Mar. 28, 1936 2,037,231 Heintz Apr. 14, 19362,099,531 Passarge Nov. 16, 1937 2,141,677 Ziegenbein Dec. 27, 19382,262,901 Murphy Nov. 18, 1941 2,272,374 Kallmann et a1. Feb. 10, 19422,351,895 Allerding June 20, 1944 2,446,017 McArthur et a1. July 27,1948 2,462,020. Craig Feb. 15, 1949 2,489,873 Thorson Nov. 29, 19492,508,979 Van Gessel May 23, 1950 2,544,104 Ponte Mar. 6, 1951 2,562,163Hiensch et al. July 31, 1951 2,570,248 Kelley Oct. 9, 1951 2,647,218Sorg et a1. July 28, 1953 FOREIGN PATENTS 502,101 Great Britain Mar. 10,1939 589,977 Great Britain July 4, 1947

